1. Field of the Invention
The present invention relates to a power-driven nailing machine driven by power such as compressed air, and especially to a power-driven nailing machine for nailing a roof material, such as an asphalt roofing with tar applied on a surface thereof, onto a base material of a roof.
2. Related Art
There is a case where a power-driven nailing machine driven by power such as compressed air is used for a nailing operation that a roof material such as an asphalt roofing formed in a sheet shape is nailed onto a base material of a roof. In the power-driven nailing machine, a striking mechanism such as a cylinder or a piston is accommodated a housing, and a nose portion, including an injection port for driving and guiding a nail, is mounted in a leading end of the housing. A driver for striking the nail is slidably accommodated in the injection port. The driver is driven within the injection port by the striking mechanism, thereby the nail supplied in the injection port is struck out of the injection port in the direction of the leading end of the injection port of the nose portion. As a result, a roof material such as an asphalt roofing set in the leading end of the nose portion is nailed on a base material of a roof. In the asphalt roofing, a tar is previously applied on the surface thereof for waterproofing.
When an operation of nailing the asphalt roofing with tar applied on the surface thereof is performed by the power-driven nailing machine under a condition that an air temperature is high or a sun blazes overhead and thus it is very hot, there is a possibility that the tar melted by heat can adhere to the leading end portion of the nose portion or to the leading end of the driver. In this case, when the driver returns again to the original top dead center after it is driven down to the bottom dead center by compressed air, the tar adhered to the nose portion can be pulled into an inside of the nose portion. Then, when the driver is driven repeatedly for a long time, the tar can adhere to and accumulate on an inner wall surface of the injection port of the nose portion to thereby increase the sliding resistance between the driver and nose portion. As a result, it becomes impossible for the driver and piston to return to their initial positions. That is, there can occur a poor operation phenomenon. In order to cope with the above phenomenon, JP-A-10-309703 discloses a nailing machine in which an outside diameter of the leading end portion of the driver is set smaller than the inside diameter of the injection port of the nose portion and the driver is structured such that it can be loosely guided through a driver guide hole and thus can be vibrated within the injection port in the striking or nailing operation. Thereby, in the nailing machine of JP-A-10-309703, the tar adhered to the inner wall surface of the injection port of the nose portion can be scraped and dropped out in the leading end direction of the injection port by the leading end portion of the driver vibrated within the injection port in the nailing operation.
By the way, there are power-driven nailing machines in which a contact member placed so as to project in the leading end direction of a nose portion is contact with a member to be nailed, and is thereby slidingly moved along the nose portion. In the power-driven nailing machine, an activation device is actuated by the slidingly moving contact member to thereby start the nailing operation. The nose portion formed in a cylindrical shape is loosely fitted with the inside of the contact member formed in a cylindrical shape to thereby slide and guide the contact member on the outer peripheral surface of the nose portion. When the nose portion is pressed against the member to be nailed, the contact member is contacted with the member to be nailed and is slided along the nose portion to thereby operate the activation device including a trigger lever or the like, so the nailing machine can be started.
In such nailing machine including the contact member which can be slided and operated along the nose portion, when nailing an asphalt roofing, the tar moves and accumulates between the outer peripheral surface of the nose portion and the inner peripheral surface of the contact member to thereby retard the sliding operation of the contact member. Thereby, it becomes impossible to start the nailing machine or it causes a malfunction of the nailing machine. In a related art, a groove having a semi-circular-arc-shaped section and extending in a vertical direction is formed between the contact member and nose portion, so that the tar adhered between the outer peripheral surface of the nose portion and the inner peripheral surface of the contact member can be removed along the groove. However, the tar cannot be removed completely by the related art. Therefore, in the related nailing machine, it is necessary to frequently carry out an operation in which the leading end portion of the nose portion and contact member are cleaned with gasoline or the like to thereby remove the tar adhered between them. Also, if the tar adhered to the nose portion is left overnight, the tar hardens and it is difficult to remove such hardened tar. Therefore, a trouble some cleaning operation must be executed after every end of daily nailing operation.